During the past decade there has been an explosion in the number of nanoparticulate drugs or drug delivery systems being explored, developed and marketed for the treatment and prevention of human diseases. While the potential dangers of drug administration in pregnancy are well known, there are circumstances where the benefits of maternal drug administration are perceived to outweigh the risks to the fetus. Hence, the administration of potentially harmful drugs in pregnancy is surprisingly common. Nanoparticulate delivery systems offer a potential avenue for delivering therapeutics to maternal tissues with minimal risk of incidental fetal exposure, depending on the ability of the nanoparticle in question to cross the placenta. As the conduit to the fetus, the placenta is both a drug target and a drug barrier, as well as a potential target of any toxicity. Limited studies on this topic show considerable uncertainty regarding the transplacental passage of nanoparticles, and our understanding of the criteria that determine transferability is poor. Despite the fact that the toxicity caused by environmental and man-made nanoparticulates has been widely studied in various organ systems, data on the effects of maternal nanoparticle exposure on human fetal tissues are lacking, although studies in rodents indicate that caution is justified. In this review, we examine the evidence relating to the potential toxicity of nanoparticles in pregnancy, the ability of the placenta to take up and transfer nanoparticles to the fetus, and the theoretical benefits and risks of administration of nanoparticle-based therapeutics in pregnancy.